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Emergency Systems Save Tens of Thousands of Lives

Sunday, 01 January 2012

NASA Technology

Shortly before midnight on September 21st, 2010,
the small fishing boat Ebby Luz started taking on
water. In immediate danger and 8 miles from the
shore, its crew activated an emergency beacon that began
transmitting their distress signal, identity, and location.
Within minutes, the Coast Guard was notified and
launched a helicopter to the coordinates received from
the alert. Even though the vessel had already sunk by the
time help arrived, and despite it being pitch dark, the
rescuers were able to locate and save both crewmembers
from the water.

These two sailors were among the 295 people in
the United States saved through the NASA-developed
Search and Rescue Satellite Aided Tracking (SARSAT)
system in 2010. Since SARSAT was introduced in 1982,
nearly 7,000 have been saved in the United States alone.
Worldwide—the international effort is known as Cospas-Sarsat—over 30,000 people have been rescued as a result
of these emergency beacons and the satellite/ground-station
system they rely on.

SARSAT had its beginnings in a tragic 1972 plane
crash in Alaska that resulted in the deaths of two US
congressmen. The plane’s disappearance sparked a 39 day
search over 300,000 square miles, but to this day the spot
of the crash remains undiscovered.

At the time, emergency communications for crashed
or stranded airplanes were limited to beacons that transmitted
a signal at 121.5 MHz, which is in the middle of
an aircraft’s radio band. Pilots worldwide left their plane’s
radio tuned to that frequency when not in use, in the
hopes that distress signals might be picked up by someone
flying overhead.

Though better than nothing, there were critical
problems with this system, explains David Affens, manager
of the Search and Rescue Mission Office located at
Goddard Space Flight Center. “Even though there are
many airplanes flying at any given time, the territory they
actually cover is sparse. And even when a pilot did pick
up a signal, those early beacons gave no intelligence—no
location or identification. It was just a simple tone that
indicated trouble,” he says.

Following the Alaskan plane crash, Congress directed
that an effort be made to find a better technology for
locating the sources of distress calls—an effort that NASA
led. In the latter half of the 1970s, NASA and several
other international organizations experimented with the
use of satellites to detect and locate emergency beacons.

Satellite tracking of distress signals offered several
advantages over the original “monitoring the radio”
system. Most importantly, relatively few satellites could
provide near-global coverage, ensuring that many more
distress calls were heard. And because of the motion of
the orbiting satellite, the signal frequency changes as the
satellite passes the location of the beacon (this is known
as the Doppler effect), meaning that even a simple tone
could now be processed to provide location data for rescuers.
“You can do some interesting Doppler calculations
with the signal that gets captured,” says Affens. “The
measurements we make from the change in frequency as
a function of the satellite’s position give us a pretty good
idea of the signal’s location.”

Following testing, the United States, Canada, France,
and the Soviet Union signed an agreement in 1979 to
develop what would become Cospas-Sarsat, an internationally
recognized configuration of beacons, satellites,
and ground stations—as well as the technology behind
each of these components—to receive and process distress
signals.

SARSAT, the part of the system operated in the
United States by the National Oceanic and Atmospheric
Administration (NOAA), began official operations in
1982. Within days, a downed aircraft was detected and its
passengers rescued using the system, which Affens says was
a confirmation of SARSAT’s viability and importance.
Following a set of international agreements—including
commitments to run the system for many years, as well as
to make its benefits available to all states on a nondiscriminatory
basis—Cospas-Sarsat was declared operational in
1985.

Technology Transfer

The first generation of the technology used satellites
in low Earth orbits (LEO) to detect signals transmitted at
the same 121.5 MHz frequency used by airplanes, which
were repeated by the spacecraft to designated ground stations
for processing. For the satellite component of the
system, NASA could utilize spacecraft that had other
primary missions. But in order to establish the beacon and ground station components, NASA enlisted the help of commercial entities, including Techno-Sciences Inc.
(TSi), of Beltsville, Maryland, which won multiple contracts
with Goddard to create the first operational ground
stations.

This first system provided near global coverage for
emergency beacons, but it still had limitations. Because
the LEO satellites in use move at high speeds relative
to the distress beacon on the surface, a stranded person
has at most a 15-minute window to be heard by a passing
satellite. Additionally, the orbits of present satellites
equipped to handle distress signals are spaced apart such
that someone in distress might only encounter one or two
satellites over the course of several hours—potentially
creating long delays before the transmission is picked up.

The system has been augmented over the years to
include geostationary satellites—or satellites whose orbit
matches the rotation of the Earth, making them appear
stationary from the ground—and an improved beacon
signal, both developed at NASA. While these satellites
cannot transmit Doppler data, they can alert rescuers that
a beacon has been activated. They also have the capability
to receive signals transmitted at 406 MHz, a frequency
that allows the beacon to send digitally encoded information,
such as a GPS location and personal identification,
giving rescuers greater awareness of the situation.

Despite the aid of geostationary satellites, however, the
potential delays in signal reception remained. To resolve
this weakness, NASA spearheaded an effort to create what
became the Distress Alerting Satellite System (DASS).
DASS enhances the existing system by incorporating
search and rescue instruments on global positioning
system (GPS) satellites. Currently, there are more than
two dozen satellites in the GPS constellation in mid-
Earth orbit (MEO), and they are distributed such that
every point on the Earth is visible to at least four satellites
at any given time.

DASS is designed to reduce the time from beacon
activation to rescue by acquiring as much data as possible.
Whenever a distress signal is relayed by multiple MEO
satellites to a ground station, time and frequency measurements
are made and combined to calculate the beacon’s
location. “With just one burst of the beacon, you get two
different data sets from each of at least four satellites,”
explains Affens. “Each one alone is sufficient to give you
an accurate location. And with each additional burst you
get even more data to refine the location further.”

The high quantity of data received means that rescuers
have the luxury of being picky about the quality of the
data they rely on. With so much information available,
the system can simply throw out any bad data, improving
the precision of calculations.

As each generation of SARSAT has been developed by
NASA, commercial partners like TSi have contributed
hardware and technology to support development and
ongoing operations. TSi designed and installed the DASS
prototype ground station for the Search and Rescue
Laboratory at Goddard, and the company was selected by
NOAA in 2009 to build the first DASS ground station
capable of becoming operational in the United States,
which will be installed in Hawaii.

Gilmer Blankenship, chairman of TSi and a professor
at the University of Maryland College Park, says that
these partnerships help put TSi in position to compete
in the global market for search and rescue components. “We’ve now built stations in the United States, India, Spain, Norway, and about 15 other countries for a wide
range of organizations. For us, this was a direct spinoff
of NASA technology that turned into a commercial business,
which we still participate in today,” he says.

Benefits

The long reach and overall effectiveness of the Cospas-Sarsat system was demonstrated in 2010 through the high
profile rescue of Abby Sunderland. Sunderland, 16 years
old at the time, was attempting to become the youngest
person ever to sail solo around the world. When her
boat was severely damaged in a storm in the middle of the
Indian Ocean, Sunderland found herself stranded in one
of the most remote parts of the globe: she was 2,000 miles
from the nearest land and in a region where few other
vessels pass by.

Before leaving, Sunderland had been given a personal
beacon by one of NASA’s commercial partners, which was
now her only chance to call for help. Less than 10 minutes
after she activated the device, the signal was received,
Sunderland’s identity and location were processed, her
parents were contacted, and authorities began making
arrangements for her rescue. A French fishing vessel,
more than 400 miles away at the time, was directed to
Sunderland’s precise location and picked her up. “I don’t
think it could have been done any faster,” she says.

Because she was an adventurer looking to break a world
record, Sunderland’s rescue brought a lot of attention to
Cospas-Sarsat. Many other adventurers, whether pilots,
sailors, or those climbing mountains or hiking in remote
terrain, have likewise been rescued from a recreational trip
gone awry. Nevertheless, most rescues—on average more
than six people per day—involve fishermen, pilots, and
others in remote areas who are putting their lives at risk in
order to make a living.

“Sunderland is a great example of why you need this
system, but the vast majority of those using it are people
conducting their everyday business,” says Affens. “We get
reports of these rescues weekly, and they are great stories.”

Today, 41 countries participate in the operation
and management of Cospas-Sarsat, ready to respond to
any one of the over 1 million beacons registered and in
use worldwide. Between more ground stations—many
of which to be built by TSi—and satellites that will be
linked, the system will continue to provide a great deal of
redundancy, which is a good thing for those receiving and
interpreting distress signals.

Blankenship is happy that TSi has had the opportunity
to be part of the ongoing project. “This is an example of
something NASA does that, while important, is very low
visibility compared to other missions. It might not make
the front page, but on the other hand I’ve met some of
the 30,000 people who have been saved by this system.
And I can tell you that, for them, it’s a very big deal.

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